124 THE MECHANISM OF ABSORPTION AND TRANSLOCATION 



to attain a given purpose, and by changes or processes of some such 

 character as described above, to cause substances to accumulate in 

 isolated cells, or to induce translocation across isotonically osmotic tissue 

 aggregates. 



In all cases, osmotic exchanges are correlated and regulated by the 

 vital activity of the organism. Both the formation of the plasmatic 

 membranes, as well as any modification of their diosmotic properties which 

 may arise later, are the work of the living organism, which also initiates 

 those intra- or extra-cellular changes to which the continuance of exosmosis 

 or endosmosis is to be ascribed, and similarly the substances which render 

 the passive secretion of aniline dyes or other substances possible are 

 products of the metabolism of the absorbent organism. 



By the employment of these means singly or in combination, the 

 plant is enabled to fulfil all demands made upon it. We shall frequently 

 have occasion to point out, in dealing with the phenomena of translocation 

 and metabolism, how the processes involved are connected with and 

 regulated by the osmotic properties and powers of passive secretion, &c. 

 possessed by the regions or tissues concerned. The intimate correlation 

 existing throughout the entire plant is such as to warrant the assumption 

 that the osmotic properties utilized by the organism may be influenced and 

 modified in the most various ways by the operation of external agencies 

 upon the plant, as well as by ontogenetic development. 



The power of the cell to retain certain substances and reject 

 others is of fundamental importance. Unless the final products of meta- 

 bolism (CO 2 , alcohol, &c.) are continually removed, the vital activity 

 of the plant soon ceases. Moreover, by continued diosmotic removal 

 of a product, a reaction, which is at first trifling or imperceptible in amount, 

 may frequently, owing to the influence of mass in chemical reactions, be 

 continued to completion. 



This again can be demonstrated by means of the accumulation of methyl- 

 blue in a cell of Azolla or Lemna,ter the stain is permanently retained while 

 the cell remains in pure water, but if the plant is placed in a large quantity 

 of a o-oi per cent, solution of citric acid, the colouring substance is gradually 

 withdrawn from the cell and in one to a few days has entirely disappeared 1 . 

 On penetration, the acid decomposes a fraction of the tannate of methyl- 

 blue, and could do no more were it not that the citric acid salt produced 

 is continually being diosmotically removed by the comparatively infinite 

 volume of water outside. As this process continues, the complete removal 

 of the pigment substance is finally assured, while the tannin remains 

 behind in the cell, which is capable therefore of again accumulating 



1 Pfeffer, Unters. a. d. Bot. Inst. z. Tubingen, 1886, Bd. II, p. 386. The best material to use is 



Lemna minor. 



